Method of production and production facility of high strength cold rolled steel sheet excellent in chemical convertibility
a production facility and cold rolled steel technology, applied in the direction of manufacturing tools, heat treatment equipment, furnaces, etc., can solve the problems of inability to expect any great recovery, bald spots remained, and cost of facilities or installation space, and achieve excellent chemical conversion. , the effect of high strength
Active Publication Date: 2014-09-16
NIPPON STEEL CORP
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Benefits of technology
The invention proposes a method to prevent oxidation of steel sheets during the continuous annealing process. This is achieved by deliberately exposing the steel sheet to an oxidizing atmosphere in the cooling zone, which usually holds a reducing atmosphere. This process oxidizes the surface of the steel sheet, picks off any oxide film and iron oxide film through pickling, resulting in high-strength cold-rolled steel sheets that are excellent in chemical convertibility, even if the contents of certain elements such as silicon, manganese, etc., are high.
Problems solved by technology
Therefore, to remove the residual Si or Mn oxide film, the practice has been to strengthen the pickling of the sheet when leaving the annealing furnace, specifically, to lower the running rate from 100 mpm to 30 mpm and to raise the pickling temperature from 70° C. to 80° C., but the Si or Mn oxide film continued to remain and “bald spots” remained and became a problem in chemical conversion.
Even if securing enough dipping time in the pickling tank, it is not possible to expect any great recovery in the running rate due to the “bald spots” remaining.
Further, there were major problems such as the costs of the facilities or the installation space.
Method used
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[0101]The inventors used four types of high strength steel sheet of the steel types A to D to run tests. The annealing was all carried out using a continuous annealing furnace under common conditions of annealing conditions (85° C.-60 sec, 10% hydrogen-bal. nitrogen, dew point-40° C.) and gas cooling conditions (5% hydrogen-bal. nitrogen, dew point-60° C.). Further, the oxidation conditions, pickling conditions, and plating conditions are summarized in Table 1.
[0102]Steel Type A: Si: 0.7%, Mn: 2.8%
[0103]Steel Type B: Si: 1.0%, Mn: 1.8%
[0104]Steel Type C: Si: 1.3%, Mn: 1.2%
[0105]Steel Type D: Si: 1.8%, Mn: 1.5%
[0106]
TABLE 1OxidationPicklingconditionsconditionsPlatingExample13% hydrogen-80° C.Ni-platingbal. nitrogen,A pickling bydew point 30° C.5%-hydrochloric20.1% hydrogen-acidbal. nitrogen,Dipping for 5dew point 50° C.sec3atmosphere, dewpoint 5° C.Comparative43% hydrogen-Examplebal. nitrogen,dew point −50° C.510% hydrogen-bal. nitrogen,dew point −20° C.
[0107]Note that the positions ...
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Abstract
A method using a continuous annealing furnace where a cooling method of a cooling zone including part or all of the temperature range of the steel sheet of 600 to 250° C. following the heating for recrystallization is one or more of gas cooling, effusion cooling, and cooling pipe cooling, or a joint cold rolled steel sheet / hot dip galvanized steel sheet facility having such a continuous annealing furnace, to continuously anneal cold rolled steel sheet to produce high strength cold rolled steel sheet, characterized by exposing the steel sheet surface to an iron-oxidizing atmosphere in the steel sheet temperature range to make the surface oxidize, pickling the sheet at the outlet side of the annealing furnace, then iron- or Ni-plating the sheet to 1 to 50 mg / m2.
Description
TECHNICAL FIELD[0001]The present invention relates to a method of production able to produce a high strength cold rolled steel sheet excellent in chemical convertibility even when increasing the contents of Si, Mn, etc. along with the increase in strength and a production facility for realizing the same.BACKGROUND ART[0002]In the past, when producing high strength cold rolled steel sheet, a continuous annealing furnace facility charging inert gas into a furnace atmosphere (see FIG. 11) or a joint cold rolled steel sheet / hot dip galvanized steel sheet facility having such a continuous annealing furnace (see FIG. 12) has been used.[0003]In the continuous annealing furnace facility shown in FIG. 11, in general, cooling using water such as mist cooling and water dip cooling, gas cooling spraying cooled atmosphere gas and / or roll cooling which cools by contact with a cooling medium running through the inside are / is used for the cooling zone.[0004]The joint cold rolled steel sheet / hot dip...
Claims
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IPC IPC(8): C23C8/10C21D9/46C21D9/573C22C38/00C22C38/02C22C38/04C22C38/06C23C2/02C23C22/78
CPCC23C22/78C23C2/02C22C38/001C21D9/573C22C38/06C21D9/46C22C38/04C22C38/02C23G1/08C23C2/0222C23C2/0038C23C2/024C23C2/022C23C2/0224C23C2/06C23C2/29
Inventor MATSUMURA, KENICHIROYANABA, KOHJIYASUDA, YUUKI
Owner NIPPON STEEL CORP